Since a hydrogenated norbornene ring-open polymer has excellent transparency and a low birefringence, application of the polymer as a resin material for optical lenses or optical sheets has been proposed (Patent Documents 1 and 2). In addition, since the polymer exhibits excellent fluidity in a molten state and also has excellent elusion properties and chemical resistance, application of the polymer as a resin material for other than optical application such as a packing film, a medical container, and the like has been proposed (Patent Documents 3 and 4). However, since many hydrogenated norbornene ring-open polymers are amorphous, their moisture proofing properties, anti-sebum properties, solvent resistance, and the like are insufficient. Improvement of these properties has been desired.
As a hydrogenated norbornene ring-open polymer having crystallinity (i.e. having a melting point), crystalline hydrogenated products of a norbornene ring-open polymer containing a repeating unit of norbornene monomers having 3 or more rings are known (Patent Documents 5 to 7). Resin films or sheets obtained from the hydrogenated norbornene ring-open polymers described in these documents are excellent in transparency, heat resistance, and chemical resistance, as well as mechanical strength. However, these crystalline hydrogenated norbornene ring-open polymers have poor solubility in solvents and deposit from the solvent after hydrogenating the ring-open polymer, sometime making it difficult to sufficiently purify the polymer by removing residual catalysts and the like. In addition, the film molded from the hydrogenated norbornene ring-open polymer did not fully satisfy the requirement for moisture permeability.
Non-patent Documents 1 and 2 propose hydrogenated norbornene ring-open polymers possessing a certain degree of crystallinity. However, these documents do not specifically describe the properties of the polymers. Among the specifically disclosed polymers, those having a high molecular weight and a narrow molecular weight distribution exhibited difficulty in controlling the film thickness when the film is produced. Films made from the polymer having a small molecular weight had a small tensile breaking elongation, indicating that the polymer has a problem of mechanical properties when made into a film. Furthermore, since the hydrogenation degree is not necessarily enough, molded products made from the polymer are easily burned.
Along with high integration of semiconductor chips and liquid crystal display devices in the electronic fields, quality degradation due to mixing of contaminants such as fine particles, moisture, and organic substances during the manufacturing process poses a serious problem. Therefore, it is necessary to store and transport precision substrates such as a silicon wafer substrate, a liquid crystal display substrate, and the like used for production of these parts under an environment where the above-mentioned contaminants are reduced to an amount as small as possible. For this reason, a method of storing and transporting these precision substrates in a state isolated from the outside environment by utilizing an airtight container of which the inside is highly purified (a wafer carrier for semiconductor production) is used.
A method of filling the container with clean air or an inert gas in order to prevent contaminants such as fine particles from adhering to the precision substrate stored in the container has also been employed. In order to respond to the recent demand for further low contamination, a method of evacuating the internal atmosphere of the container to provide vacuum or reduced pressure conditions has been proposed. The container of which the internal atmosphere is evacuated not only must be airtight and pressure resistant, but also the container material itself must not discharge contaminants such as moisture and organic substances.
As a container satisfying these requirements, a metal container and a container made from a thermoplastic resin having excellent chemical resistance and low water absorptivity such as polypropylene (PP), polytetrafluoroethylene (PTFE), perfluoroalkoxy fluororesin (PFA), or the like are known.
However, a metal container is heavy, cannot allow observation of the precision substrates stored therein, and has a high manufacturing cost. PP is opaque and has poor dimensional accuracy and heat resistance. PTFE is not only opaque and has poor dimensional accuracy, but also does not allow injection molding, making mass production difficult. The PTFE product is therefore expensive. PFA has insufficient transparency and poor dimensional accuracy, and it is difficult to synthesize PFA and to manufacture the product in a large scale. The PFA product is thus also expensive.
As a molding material which solves these problems, a thermoplastic norbornene resin which can be molded by injection molding and has excellent heat resistance, moisture resistance, chemical resistance, transparency, and the like is attracting attention in recent years.
For example, a thermoplastic resin container formed from a cycloolefin resin is proposed in Patent Document 8. The Patent Document 8 describes that a hydrogenated norbornene ring-open polymer is preferable as a cycloolefin resin due to the small content of impurities such as low molecular weight components, catalyst residues, metals, and the like in the resin and also due to high transparency.
Patent Document 9 proposes a material for producing semiconductors formed from a thermoplastic saturated norbornene resin having a contact surface of 18.6 kgf/cm2 at a load deflecting temperature of 70° C. Patent Document 10 proposes a container for precision substrates made from a thermoplastic resin and having one or more components which have specific properties. A hydrogenated norbornene ring-open polymer and the like are given as a preferable thermoplastic resin.
However, when a wafer carrier for semiconductor production is fabricated using the thermoplastic resin molding material described in these Patent Documents, there is a problem that the surface of the semiconductors in the carrier is contaminated with an organic substance discharged from the molded article. In addition, when the wafer is inserted into or removed from the carrier, the carrier may be caused to come into contact with the wafer and produce a resin powder (foreign matter) which contaminates the wafer.
In the field of medical supplies and food packing, packing materials for medical supplies such as an infusion solution bag, a blood bag, a bottle for medicine, a cell used for analysis, and a medical test tube, as well as packing materials for food such as bean paste, soy sauce, and mayonnaise are widely used. These packing materials are required to possess transparency, chemical resistance, impact resistance, capability of being repeatedly sterilized, steam barrier properties, and the like. In order to satisfy these requirements, a number of packing materials for medical supplies and foods using a synthetic resin such as a thermoplastic norbornene resin having excellent transparency or chemical resistance have been proposed.
For example, Patent Document 11 proposes a packing container for medical supplies and foods of which the wall is made of a multilayer laminate, at least one layer being made of a thermoplastic norbornene polymer.
Patent Document 12 discloses a molded article prepared by laminating a gas barrier resin layer of a partially saponified polyvinyl acetate on the surface of a thermoplastic norbornene resin molded article.
However, all the thermoplastic norbornene resins described in these Documents are amorphous materials which have insufficient impact resistance and oil resistance when used as a packing material for medical supplies. Moreover, the packing container for medical supplies and foods described in Patent Document 11 has poor steam barrier properties. The molded article described in Patent Document 12, in which thermoplastic norbornene resin has poor steam barrier properties, has a problem of degradation of oxygen barrier properties due to denaturing of the gas barrier resin layer by water in a high temperature and high humidity environment.
On the other hand, Patent Document 13 proposes a film or a sheet obtained by molding a norbornene ring-open polymer having a melting point or a hydrogenated norbornene ring-open polymer having a melting point obtained by hydrogenating the carbon-carbon double bonds in the ring-open polymer.
However, the hydrogenated dicyclopentadiene ring-open polymer having a melting point which is specifically disclosed in this Patent Document can be molded only with difficulty due to unduly high melting point of 270° C. or more. In addition, the resulting molded product has poor steam barrier properties and mechanical properties such as impact resistance.
Blister molded articles such as a press-through package (PTP) have been manufactured by producing a resin sheet (sheet for blister mold) and molding the sheet by a heat molding method such as vacuum molding or pressure molding.
Outstanding moldability, damp proofing (steam barrier) properties, impact resistance, oil resistance, and the like are required for such blister molded articles. In order to satisfy these requirements, a number of blister molded articles made of a synthetic resin such as a thermoplastic norbornene resin have been proposed.
For example, Patent Document 14 discloses a press through package (PTP) with a packed material contained therein. The package is prepared by enclosing the material to be packed in a pocket provided on a sheet of a thermoplastic norbornene resin and blocking the pocket opening of the sheet with another sheet.
Patent Document 15 discloses a multilayer sheet for packing drugs requiring high moisture proofing properties. The sheet is made from (A) an amorphous polyolefin having a heat distortion temperature of 100° C. or less, which is a copolymer of a product of the Diels-Alder addition reaction of cyclopentadiene (or a derivative thereof) and norbornadiene (or a derivative thereof) and an unsaturated monomer and (B) polypropylene, wherein a layer of the polypropylene (B) is laminated on at least one side of the amorphous polyolefin resin layer (A).
However, all thermoplastic norbornene resins described in these Documents are amorphous resins, which may sometimes have insufficient mechanical strength, heat resistance, and oil resistance when used as a blister molded article. The PTP described in Patent Document 14 may become whitened by adhesion of sebum during use, and the high moisture proofing multilayer sheet for packing drugs described in Patent Document 15 has a problem of poor steam barrier properties.
In order to obviate these problems, Patent Document 16 proposes a film or a sheet formed from a norbornene ring-open polymer having a melting point or a hydrogenated norbornene ring-open polymer having a melting point obtained by hydrogenating the carbon-carbon double bonds in the ring-open polymer.
However, the hydrogenated dicyclopentadiene ring-open polymer having a melting point which is specifically disclosed in this Patent Document can be molded only with difficulty due to unduly high melting point of 270° C. or more. In addition, the resulting molded product may have poor steam barrier properties and mechanical properties.
On the other hand, Patent Document 17 discloses a blow-molded article prepared by blow molding of a norbornene polymer having a melting point. The norbornene polymer having a melting point described in Patent Document 17 is a crystalline polymer. Various hydrogenated ring-open polymers of norbornene monomers are mentioned as the norbornene polymer having a melting point in Patent Document 17. However, the Document specifically describes only a hydrogenated ring-open polymer of dicyclopentadiene. The hydrogenated dicyclopentadiene ring-open polymer is a polymer having a high melting point of 200 to 400° C.
Therefore, in the blow molding process shown in examples of Patent Document 17, the hydrogenated dicyclopentadiene ring-open polymer is extruded from a biaxial extruder at a barrel temperature of 290 to 300° C. and a die temperature of about 320° C. to produce a molten parison. Molding at such a high temperature not only subjects the molding machine to a significant load, but also tends to produce resin burning (discoloration). Although the resulting blow-molded container is excellent in heat resistance, oil resistance, chemical resistance, and the like, the steam barrier properties are not necessarily sufficient. In addition, since the hydrogenated dicyclopentadiene ring-open polymer can be dissolved in an organic solvent only with difficulty, purification of the product is difficult and the product has a problem of elution of metals derived from the catalyst.
The above-mentioned Non-patent Document 1 reports that a crystalline thermoplastic polymer with a melting point of 141° C. was obtained by hydrogenating an amorphous polynorbornene having a trans content of 80% and a weight average molecular weight (Mw) of 2,000,000.
Non-patent Document 2 reports the crystal structure and melting point of a block copolymer of hydrogenated polynorbornene and hydrogenated polyethylidene norbornene (hPN/hPEN).
However, since the hydrogenated norbornene ring-open polymers disclosed by Non-patent Documents 1 and 2 have a large number average molecular weight (Mn) and a narrow molecular weight distribution (Mw/Mn), it is difficult to precisely control the thickness of the container formed if the polymers are molded by blow molding. In fact, neither Non-patent Document 1 nor Non-patent Document 2 describes production of a molded article by blow molding of the hydrogenated polymers.    [Patent Document 1] JP-A-60-26024    [Patent Document 2] JP-A-9-263627    [Patent Document 3] JP-A-2000-313090    [Patent Document 4] JP-A-2003-183361    [Patent Document 5] JP-A-2000-201826    [Patent Document 6] JP-A-2000-393316    [Patent Document 7] JP-A-2006-52333    [Patent Document 8] JP-A-11-74337    [Patent Document 9] JP-A-2002-217279    [Patent Document 10] WO 2003/021665    [Patent Document 11] JP-A-4-276253    [Patent Document 12] JP-A-2002-127315    [Patent Document 13] JP-A-2002-194067    [Patent Document 14] JP-A-6-278706    [Patent Document 15] JP-A-7-178884    [Patent Document 16] JP-A-2002-194067    [Patent Document 17] JP-A-2002-249554    [Non-patent Document 1] Polymer International, Vol. 34, pp. 49-57 (1994)    [Non-patent Document 2] Macromolecules, Vol. 37, pp. 7278-7284 (2004)